Sound reproducer



Patented Mar. 16, 1926. y 1,577,254

UNITED STATES tPATENT OFFICE.

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To all whom t may concern.' subjected to conditions such that it wouldBe it known that I, HARVEY C. Haras, a be somewhat highly and uniformlydamped 55 citizen of the United States, andaresidentpf over its lwholesurface, the reproduction Washington, District of Columbia, have 1n-Would come still nearer to being perfect,

5 vented certain new and useful Improve- 'especially if the diaphragmcan be made to ments in a, Sound Reprodueenof, which the have smallinertia so that the restoring following is a specification. forces aresmall. i

My invention relates to a means for trans- An object of this inventionis to rovide a y forming electrical energy into sound energy, receiverhavin a conical shaped diaphragm and more particularly toa soundvreceiver or with uniform y distributed driving and'` reproducer. damp gforces which Will accomplish the In Aorder to transform electricalenergy above advantages. p 65 into sound energy without distortion -itbe- With this and' other objects in view the comes necessary to furnishsome mec anism invention consists in the construction, comcarrying amovable or vibrating member bination and arrangement of parts as willthat will be caused to move by the luctuatbe hereinafter described.

ing electrical current, and insuch a way Referring to the accompanyingdrawing 7 that the pressure uctuations of the air forming part of thisspecification and in caused by the vibrating movements of this which theligure illustrates a cross-sectional member will have the samecharacteristics as view of a sound receiver, 1 indicates a cylinthecurrent causin this member to move. drical member forming part ofa'magnetic This requires that t emovable member shall circuit consistingof magnetic material elebe of such a design or shall be subjected toments 1, 2, 3, and 4, and having a conedforces in such a way that itwill not break shaped upper portion and reduced lower 5 up4 into partialor harmonic vibrations and portion. The reducedportion of this memnshall be so designed or so damped that all ber seats ina ring 2 which isprovided with vibrations cease when the current Ailuctuaa passageway forconductors 9. 3 is a cylin- 5 tions stimulatino` the motion cease..drical outer member connecting the rin 2l These desirable conditionshave been apand a conical air-gap between 1 and 4. e proached by the useof conical shaped diamagnetic circuit can be energized by a diphragmsand by damping the motion of Hat rect current carried by conductors 9through diaphragms over those regions where the coil 5 or the metal ofthe circuit can be made 85 harmonic loops occur, but usually the ofmagnet steel such that the magnetic method of driving the diaphragm froma flux of the circuit will be maintained after point or small regionabout its center is so being once established. Coil 6, which isfavorable to the establishment of harmonics Wound upon the coned surfaceof member 1, in the diaphragm that the damping required carries t toeliminate them must be so effective that transferred into sound energy,and which is the motion of the diaphragm as a whole is led to it bywires 8 passing through memgreatly hindered and the device becomesber 1. A thin conical shaped diaphra very insensitive. preferably madeof aluminum, is iexi ly The tendency of a diaphra m to break upsuspended between 4 and the coil 6 by a' 95 into harmonic vibrations woud be almost nil ilange 11 which is secured to the member 4 if thedriving force could be uniformly disby screws 10. tributed over thewhole surfaceinstead of The principle of operation of the device isbeing concentrated at a point or small reas follows: gion near itscenter. It 1s evident, also, if The fluctuating telephonie currents 100the diaphragm could have the form of a through coil 6 generatesubstantial eddy curcone so that its rigidit would tend to prerents inthe aluminum conical vdiaphragm vent the formation o harmonics by suchbecause of close electrical coupling be`ween small tendency as might`evist, the device thesel elements. These eddy currents circue telephoniecurrent that is to be Vwould come very near to giving true re rolateabout the diaphragm in a direction l duction. And if the diaphragm coulbe perpendicular to its axis, and are of uniform density throughout thediaphragm 1s-`r if the windings of coil 6 are uniforml tributed over thecone surface of mem er l.

The eddy currents traversing the coned part of the diaphragm pass erendicularly throu h the magnetic held.) ol) the coneshape air-gap, and,according to the well known laws of electro-dynamics, the conductorcarrying the current will at allpoints experience a force tending toproduce motion along a line perpendicular to both the i field strengthsubstantially uniform throughout the air-gap, and since the currentdensity ic practically uniform throughout the cone of the diaphragm, itfollows that the forces tending to urge each particle of the conical`portion of the diaphragm back and forth along an element of the conemay be made substantially uniform throughout the coned portion of thediaphragm. Moreover, the force at any and every point in this part ofthe diaphragm can be resolved into two componente, one radial to thecone and the other parallel with its axis. The components parallel withthe axis are all in one direct1on at any instant, the direction beingdetermined by the direction of the telephonie current in coil 6 at thatinstant. These forces, therefore, tend to drive the diaphragm back andforth along its axis and the driving force is uniformly distributed overthe conical surface of the diaphragm. This force is at all timesproportional to the strength of the magnetic lield in the air-gap and tothe tele phonic current in coil 6.

Since the diaphragm is both pushed and pulled bv the action of thetelephonie current and `does not depend upon restoring forces withinitself for its motion,the circular flange rovided for mounting thedtaphragm can e made very light and flexible and under such conditionsthe natural resonant frequency can be made lower than that `of thesounds which the device is designed to generate. In this way resonancepan be largely eliminated. But even if this were not done the devicecannot be highly resonant for the reason that motion of the diaphragm ishighly damped. If the diaphra' is made to vibrate either by its owninertla and restoring forces or by some other agency, the coned portionof the diaphragm y will cut across the magnetic .field of the au'- gapwith the result that eddy currents will be generated about the cone insuch a direction as to oppose its motion. Moreover, this damping effectwill be uniformly distributed over the whole conical surface of thediaphragm. This effective damping causes the diaphra m to move at alltimes in proportion to t e driving current and to stop moving when thedriving current sto s.

The forces tendin to move the diaphragm are wholly due to t e reactionof a current passing through a magnetic field and not to a variation inthe strength of one or more magnetic poles. This gives the presentinvention two advanta es: First, since its operation is independent ofvar ing the strength of the ma etic circuit, the flux of this circuitcan be rept saturated and constant and this gives the device a highpower factor by confining the flux change through the coil 6 to what itwould be if there were no iron resent. This reduces the reactance of thete ephonic circuit to a small value and at the same time practicallyeliminates the usual losses due to hysteresis. The eddy.

current losses are also greatly reduced for the reason that those set up1n the moving member are utilized for driving this member. Second, theforce driving the diaphragm is always proportional to the currentthrough coil 6, while in most sound reproducing devices of thetelephonie class the force is proportional to the magnetic flux linkagebetween the lixed and movable parts -of the magnetic circuit and this inturn is a somewhat complicated function of the current through thetelephonie coils and the relative position of the movable part of the maetic circuit. As a result, the forces ten ing to move the diaphragm arenot proiortional to the current and the character' lstics of thegenerated sound waves are not strictly proportional to thecharacteristics of the current.

Having described my invention, I claim:

l. In a device of the character described the combination of a magneticcircuit having a conical air gap, a tele honic current winding uniformlydispose on one side of said gap, and a conductive cone' diaphragmmovably suspended between said winding and the second side of said airgap and havin the angularly disposed walls thereof su stantiallyparallel with said winding.

2. In a device of the character described the combination of a lluxedmagnetic circuit having a conical air gap, a current carrying windinguniformly disposed on one side of said gap, and a conductive conediaphragm vibratorily suspended in said gap and having the angularlydisposed walls thereof substantially paralel with said windiv In adevice of the character described winding fixed in said gap, and aconductive cone. diaphragm vibratorily suspended in said gap and havingthe singularly disposed walls thereof substantially parallel with saidwinding.

4. In a device of the character described means-for creating a conicalmagnetic gap, a

conductive cone diaphragm vibratorily sus- 10 pended in said gap, :mdmeans for inducing uniformly distributed eddy currents in saiddiaphragm.

HARVEY c. HAYES.

